Fear Conditioning (FC) is a type of associative learning task in which mice learn to associate a particular neutral Conditional Stimulus (CS; often a tone) with an aversive Unconditional Stimulus (US; often a mild electrical foot shock) and show a Conditional Response (CR; often as freezing). After repeated pairings of CS and US, the animal learns to fear both the tone and training context. FC is learned rapidly, and after one conditioning session, a very stable and long-lasting behavioral change is produced which is useful for neurobehavioral, genetic, and pharmacological studies. In Trace FC the CS and the US are separated by a certain time interval. It has been shown that the frontotemporal amygdala has an important role in both acquisition and expression of conditional fear and that the hippocampus is necessary for contextual and trace FC.
Two different contexts, Context A and B, are used in FC. In the first day, the subjects are placed in Context A, and after 3 min, they receive five tone-shock pairings. The shock (0.5 mA, 2 sec) is delivered 18 sec after the end of the tone (75dB, 2 kHz, 20 sec). An empty trace interval interposes between the tone and the shock in each CS-US pairing. In the second day, mice are placed in Context B (new olfactive cue, floor texture, and visual cues) for 3 min and subsequently given three tone presentations without any shocks. In the last day of the experiment, mice are placed in Context A for 5 min without any CS and US. Freezing is defined as the complete lack of motion for a minimum of 0.75 second and the percent of freezing in each period of time are reported.
Delay Fear Conditioning
Delay Fear Conditioning (FC) is used to assess Pavlovian learning and memory in rodent models of CNS disorders. Subjects learn to associate a neutral Conditional Stimulus (CS; a tone) with an aversive Unconditional Stimulus (US; a mild electrical foot shock) and exhibit a Conditional Response (CR; freezing). After repeated pairings of CS and US, the subjects learn to fear both the tone and training context. Two different contexts are used: the Training Context is square-shaped with a metal floor used for US delivery while the Novel Context employs a U-shaped chamber whose floor and walls are covered by plastic inserts. The chambers are lit by two different types of light sources. Subjects are first habituated to the Training Context with no shock or tone. On Day 1, subjects are placed in the Training Context for a brief period, followed by tone-shock pairings. The next day (Day 2), subjects are placed in the Novel Context and only presented with tones. On Day 3, subjects are returned to the Training Context but experience no tones or shocks. The percentage of freezing during a specified time is reported. Delay FC is a useful test for neurobehavioral and genetic studies on transgenic strains of mice, and for pharmacological studies evaluating the effect of novel chemical entities on cognition.